In a communications system, signals may occur in some regular fashion. In one such system, e.g., in a pulse code modulated (PCM) system such as the Bell System T-Carrier system, analog signals may be sampled at a clock rate of 8,000 Hertz for conversion to a digital PCM character. The PCM character may be multiplexed into a time slot of 193-bit frame and the frame then transmitted at a bit rate of 1.544 megabits per second over a communications link to a receiver. The frame usually includes a framing signal and a plurality of characters, each character from a different one of a plurality of input trunks, typically 24 trunks. Thus, the PCM characters may occur in some regular fashion such as the first character in a time interval (0, T), a second character in a time interval (T, 2T), a third character in a time interval (2T, 3T), etc.
In another such system, e.g., in a television broadcasting system, it is common for a television picture scene to be sequentially scanned from left-to-right and top-to-bottom as a series of narrow horizontal scan lines somewhat in a manner analogous to the way the eye of a reader scans a page of printed material. The scanning process usually traverses 525 horizontal scan lines within 1/30 of a second to form a picture frame. Thus, television scan lines may occur in some regular fashion such as the first scan line in a time interval (0, T), a second scan line in a time interval (T, 2T), a third scan line in a time interval (2T, 3T), etc.
To digress, clearly still other regularly occurring signals may occur. However, for brevity, we hereinafter disclose our bandwidth reduction and multiplexing signal processor and system in terms of video signals such as television signals with an understanding that our processor and system are not limited to video signals but extend to signals of whatever nature that may occur in some regular fashion.
Continuing, to reduce flicker, it is common to interlace the horizontal lines of a frame. For example, the odd numbered lines could comprise an odd field while the even numbered lines could comprise an even field. The two fields then comprise the frame. Commonly, the first field is first scanned within 1/60 of a second. Thereafter the second field is scanned in the next 1/60 of a second. The first field is transmitted in one time interval followed by the second field in a second time interval whereby the lines are interlaced. It is also well known to those skilled in the art that various blanking pulses and synchronizing pulses are inserted usually at the ends of the scan lines as well as at the ends of the picture fields and frames.
In today's technology, it is common to transmit such television picture signals by way of a satellite transponder channel which commonly employs frequency modulation and has a bandwidth of about 36 megahertz (MHz). Indeed, to determine the bandwidth (BW) required for transmission, a well-known equation called the Carson equation is generally used where BW=2(.DELTA.f+f.sub.m) and .DELTA.f is the peak frequency deviation commonly 4 MHz and f.sub.m is the upper baseband frequency commonly 4.2 MHz for National Television Standard Committee (NTSC) color television pictures. The Carson bandwidth is usually quite generous and provides for the passage of sidebands that are within 10 percent of the unmodulated level. Furthermore, the typical transponder channel is about twice the Carson bandwidth.
Obviously, bandwidth is a precious resource in a communications system. With signals such as television signals using relatively large bandwidths, the art is ever looking for bandwidth reduction arrangements. For example, U.S. Pat. No. 4,215,370, issued July 29, 1980 and entitled "Satellite Video Multiplexing Communications System", discloses a communications system for distributing two distinct video programs via a single satellite channel using time division principles and for transmitting alternating lines of video information for the two video programs by a single frequency modulated carrier. The alternating lines are compacted in time and occupy a substantial portion of the synchronizing pulse period of the video lines. One line is partially repeated to reduce spurious system transient responses.
However, known arrangements for transmitting a plurality of signals on a single communications link tend to use techniques which have a debilitating effect upon the quality of the received signal.